A high power converter application, such as a PWM-based uninterruptible power supply (UPS), may require low inductance/high current inductors for power conversion circuits, such as rectifiers and inverters. In such an application, it may be desirable to maintain useful inductance to 3 times the rated current. Operational currents may include both a 50/60 Hz power component and high frequency ripple currents.
Conventional inductor designs include closed flux path and gapped (discrete & distributed) core designs. Torroidal designs may require a complex winding design, and core heat may be trapped inside such a complex winding. Winding heat may further add to core temperature, and inner winding layers may be difficult to keep cool in such designs.
Gapped EE/EI or UU/UI designs often include a large core volume with a large air gap. Difficulties in cooling often drive toward the use of a ferrite core, which may be costly due to higher core volume.
Open flux path (e.g., air core) inductors may also be used. Simple air core designs may occupy a large volume to achieve a desired inductance, which can lead to high coil resistance and losses. Multiple layers can amplify skin and proximity effect losses and can impede cooling of inner layers. Losses often exceed acceptable levels, and the return flux path (thru surrounding air) may adversely affect nearby items. Escaping radiated fields may elevate EMI levels, and adjacent sensitive electronic circuits may respond adversely to this EMI.
U.S. Pat. No. 7,205,875 to Oughton et al. describes inductor structures for use in power converters and other applications that support air cooling and may be fabricated in a relatively cost-effective manner. As shown in FIGS. 1 and 2, such an inductor may include a ferrite magnetic core 13 supported in a bobbin-like frame 11 around which one or more coils 12 are wrapped. The bobbin 11 spaces the coil apart from the core 13 to provide a coolant passage that provides air flow between the core 13 and the coil 12.